Color television system



4 Sheets-Sheet l NVENTOR m l MIL E vj TTORNEY W. D. HoUGHToN COLOR TELEVISION SYSTEM II/XXZIX July 31, 1956 Filed April 2o. 195o Riki/'63a' July 31, 1956 w. D. HouGHToN coLoR TELEVISION SYSTEM Filed April 2o, 195o 4 sheets-sheet 2 w ,Q Y H lrm.

July 3l, 1956 w. D. HoUGHToN coLoR TELEVISION SYSTEM 4 Sheets-Sheet 3 Filed April 20. 1950 nlllhvwllib m En INVENTOR ATTORNEY V E m N E n m, m Qu w wwmmm .MM m i @E ME E n WN E \JI www. M* N\\-\|\|-i|| Nw @t k3 ,E .Q h vvx.. A J Y S 1NR .h EW s A* E ,awwwmwmm July 3l, 1956 w. D. HOUGHTON 2,757,227

COLOR TELEVISION SYSTEM Filed April 20, 1950 4 Sheets-Sheet 4 Ill.

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am@ mm INQ INIWMRMN ATTO R N EY `tive cross talk balance.

United States Patent O COLOR TELEVISION SYSTEM William D. Houghton, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 20, 1950, Serial No. 157,148

Claims. (Cl. 178-5.2)

This invention relates to multi-channel signalling systems of the time division multiplex type. Though not necessarily exclusively limited thereto, the invention relates, in one aspect thereof, particularly to multiplex signal generation and sampling in a color television system. v

One of the presently-used color television systems operates according to the dot or elemental multiplex principle. A typical embodiment of such a system is shown in copending U. S. application of John Evans, Serial No. 111,384, filed August 20, 1949, and titled Color Television. According to this principle, the color information of each of a multiplicity of elemental image areas is represented by a group of successive video signals. The color-representative video signals of each elemental image area are transmitted and received successively. In this process, it is necessary to produce a composite video signal wave which has instantaneous amplitudes, at successive time-spaced intervals which are representative respectively of the component colors of successive elemental image areas. In order to reproduce an image from such video signals, it is necessary to sample the wave at times corresponding to each of the predetermined time spaced intervals. The video signal information thus derived is used to excite the image reproducing apparatus to produce light of the different component image colors.

Originally, the sampling of the composite video signal Wave was done at an early stage in the receiver. At such a stage the signal level is relatively low. Hence, such an arrangement was called a low level sampling system. It since has been determined that successful sampling of the received video signal wave may be accomplished at relatively high signal levels. Such a practice may be followed without encountering any substantial diminution of the light derived from the image reproducing apparatus or without adversely affecting the color separation. In either high or low level sampling systems, a judicial choice of parameters will produce a highly effec- In other words, the cross talk which might be expected to be produced by taking samples of the composite video signal Wave is effectively balanced out so that it does not appear 'in the linally produced signal to cause color dilution.

Presently, high level video signal sampling is preferred. One reason for this preference is the apparatus simpliiication which is made possible. Also, since only one video signal amplifying channel is required, uniform amplication of all color video signals is effected.

One high level video signal wave sampling arrangement is covered in the copending U. S. application of George C. Sziklai, Serial No. 145,420, filed February 21, 1950, and titled Color Television Receiving System, now Patent No. 2,725,418, granted November 29, 1955. In this application the video signal wave is impressed continuously, after suitable amplification thereof, upon one electron beam intensity control electrode of a cathode ray image reproducing tube. The electron beam is keyed ice on and off at the signal sampling frequency by means of pulses impressed upon the other beam intensity control electrode. The beam keying is effected synchronously With the reception of the different color video signal components. Y

Irrespective of whether the sampling of the video signal wave is effected at low or high signal levels, it is necessary that objectionable cross talk between'the signals representative of the different image colors be prevented. In a three color system, such as is most commonly used, the composite video signal wave may be developed from the individual color video signals so that the individual signals are spaced or timed relative to one another approximately electrical degrees at the sampling frequency. It has been demonstrated that the individual component color video signal waves may be so related relative to one another that, when one of the waves is at a maximum or peak value, the other two waves have substantially zero values.

Such a relationship is disclosed in a copending U. S. application of Clarence W. Hansell, Serial No. 124,034, tiled October 28, 1949, and titled Color Transmission System. The described amplitude and phase relationship of each of the component color video signal Waves to prevent cross talk is obtained, according to the teachings of the Hansell case, by making the amplitude of a high frequency sub-carrier Wave equal substantially to twice the amplitude of the video signal. A resultant Wave for each color video signal is produced in this manner. When a composite video signal wave formed of such resultant waves is sampled at times corresponding to the peaks of the individual resultant waves, the other two resultant waves have substantially zero amplitudes.

The present invention provides a time division multiplex system particularly suited for color television. Such a system is provided with improved signal generating and signal sampling facilities substantially of the same general character as the signal generating system covered by the Hansell application and signal sampling apparatus of the Sziklai application, both previously referred to.

An object of the present invention, therefore, is to provide a time division multiplex signalling system having improved signal generating and signal sampling arrangements whereby to operate more eiciently.

Another object of the invention is to provide an improved time division multiplex system especially adapted for color television, wherein the generation of a compositevideo signal wave is of such a character to provide automatically an effective cross talk balance whereby to facilitate signal sampling.

Still another object of the present invention is to provide an improved system for exciting the different color elements of an image reproducing means in synchronism with the reception of the corresponding color-representative video signals.

A further object of the invention is to provide improved apparatus for effecting high level sampling of a video signal wave in an elemental multiplex color television system.

In general, high level video signal sampling is eifected by impressing the composite video signal wave continuously upon one of the electron beam intensity control `copending Sziklai application referred to, this invention .5 maybe adapted for use with a single multi-color kinescope having one or `more electron beams. lAccording to one of the features of this invention, there is provided means whereby the color kinescope may be automatically conditioned for either black and white or color itnage reproduction. This is accomplished the A.present invention'principally by means of the self-biasing circuits of the keying tubes together with the mea'nsf'o'r supplying space current to these tubes. y

Cross talk balance is accomplishedin accordance with the present-invention byl adjusting the direct' current component'ofthevideo Vsignal samples. The adjustment `is made by controlling the Width or time durationof the samples. When the samples are passed'through "a l'ow pass iilter'having la'cutof b el'ow the's'econdlia'rinonic of the 'sampling frequencyfasine Wave isproducedyvhich has Ia I 'naximurnandtwo zero values occurring ysequentially "at Vl"2,()"xcleg"ree phase lintervals v'at the sampling frequ'ency.

The novel features that are consideredl characteristic of this invention 'are setiforth with Jparticularityin'the appended "claims The invention itself, however, both as to its organizatio'nan'd methodof' operation'fasfwell as additional: objects `-and 'advantages ythereof `wpill lvltest l befund'erstoo'd from thefoliowing'descriptibn talcen in connection with 'the accompanying drawings.

*Initliredrawingg p l-iigures z1y through 5 are curves showing 'waveforms referred'to. in explaining the' operation ofthe samplingI system;

Figurejisa circuit 'diagram of a television transmitte'r 'showing a typical embodiment 'of video signal generating'apparatus by'whi'ch to obtain` 'automatic crosstalk balance in accordance with this invention;

YFigure 7 is a circuit diagram of a television receiver showing :one embodiment of theimproved' sampling systern` of the present invention;

p Figure S'is a fragmentary circuit diagram of 'a typical keying circuit' embodying facilities according to the present invention for effectingautomatic operation'of the apparatus for -reproducing either black and VWhite or color images; and

Pigure'9 a` fragmentary view ofy a single multi-'color kinescopeas usedin conjunction with an embodiment of the invention. i

'Inorderto more fully appreciate the manner in which.

sampling o f azv'c'omposite color television video signal wave may. be' effected without sacrificing either"picture brightness'orfgood color separation,4 consideratinf'rst willl'be'giyen "to the character of thecoiposite fvideot signall wave and the manner in which it isdeveloped. and subs equentlyl vsampled Vin accordance with this, invention. Itwill4 be understood that the transmitting.appiatusmay include a television camera or pickuptubeifor'each'of theicolors in which the image'isl to be 'reproduced'.

Typicaltransmitting lstation apparatus will bei`described` in detail later. In the present case, it'wili be assumed thatfthe system is a three-color one in which.- the imageisv to be reproduced in red, green and bluecolors, for

example. The different c olorcomponents'of the televi.

sion'lrsubject' areseparated by means such asV dichroic -mirrorsorthe like and projectedrespectivelyupon the three `pickup tubes. The tubes, for example, maybe image-orthicons lwhich"function independently f'one. another 'tof develop'video signals' representative of the..

threefcolors. Each of vthese signals is independently amplified "and impressed upon a sampling unit. The transmitter samplerA operates to derive samples from each offthe threefvideo signals successively. As a result, each ofthe videosignals is convertedinto a series orl train,y

of amplitude-modulated pulses. Thel pulses representative of rthefth'ree colors are combined, so that every third pulse isfa sample from. the vvideo signal ofva. given color.

hreel serileslof` pulseshthen are combined with the conventional. synchronizing and blanking pulses-totorm 4 a complete color television signal. This signal is passed through-a low-passfilter having a'frequency cutoif which is only slightly higher than the video signal sampling frequency. Accordingly, the higher order frequency 5 components of the pulses are attenuated so that the signals derived from the low pass filters are substantially sinusoidal in form and have a-frequency substantially equal to the sampling frequency. The composite waveform derived from the filter consists of therthree'individual sine waves. derived from the respective series of pulses but trains'produced at'the transmitting station. It will be appreciated'that, Since the composite video signal wave includes 'three sinusoidal waves representingthe `three colors respectively,'it is necessary to sampl'e'this composite wave in such amanner that the desired color signal '25 isidri'vedexclusively'of any'other color signals. Originally n'or'dr to minimize cross talk'between the diiTerent color signals, relatively small Vsamples 'were taken of tlie`c`orip'siteY video signal wave at low signallevel stages offtlie receiver. When the signal sampleshad been suitably mplified'for impression upon the. color kinescopes,

thetr'ne duration of t-he samples would have been extended vby reason'of the normal operation of the signal v-ainpliiiers in failing to abruptly cutoif at the limits of the yfrequency pass bands' thereof. In this way, it was possible to' secure both good color separation and high light intensity.

However, it has been found that sampling of the compositevid'eo signal wave may be effected at high'levels without encountering objectionable cross talk or sacrific- `40 ing` lightin'tensity. Consequently, in the present case,

the'signal sampling is accomplished at a high signal level' suchl asvdirectly at the lrinescopes, for example.

ToV understand'fthe operation of a highl level sampling receiver; particular reference will now be made to Figures l -to 5 ofthe drawings. These figures illustrate hlwfa composite color video signal wavel may be produced by the multiplexing process so that, subsequently, it may be'sampledat anylevel in such -a manner that a. good cross' talkbala-nce may be achieved.

yParticular. reference will first. be made-to Figure l.

In one extreme. condition, it is assumed that the picture containsl only'a blue color component which varies -in intensity in different parts of -the,.picture. vThe` train of pulses llz'andulZ are those produced bythe blue color .55 sampler. vThisiigure also indicates by the letters 'B,

Gand-Rfthe timingof'the samplingiapparatus. These sampling events occur substantially at 120 degree intervals ratthe sampling frequency. At times B the; blue samplingfapparatus is operative. Similarly, at times G and R the green andred samplers are operative. Ac-

cordingly, in Figure'v l, it, is seen'that, in the time between the occurrence ofthev blue; pulses, no other pulses repl resentativeof 'green and/orjred components are produced.

The' bluepulses'll andf1`2 are passed through a low pass.A filter.I having a cutoff frequencywhich` is vslightly higheri'than the fundamental, but materially lower than the second. harmonic of the sampling frequency. There islderivedffrom the filter a substantially sinusoidal wave such asfthe wave 13. This wave hasa frequency which is" equal tothe. sampling. frequency.

-Since'thepulsesllfand 12 are unidirectional in character,f they are made up -of a direct current component di-3', a fundamental frequency alternating current corn- Apcnent Which is' equal to the. pulse'repetitionrate, and a` comparatively-large*number ofy harmonicsutherecf. ln'` passing through the low pass filter, the harmonics are elfectively attenuated so that only the fundamental wave such as represented by the curve 13 is produced in the output circuit. It is seen that the sine wave 13 has an alternating current axis which is displaced above the zero axis by an amount equal substantially to the direct current component dE. f

The key to the achievement of good cross talk balance in a time division multiplex system of this character is in producing the proper direct current component of the different color video `signal waves. With reference to the pulses 11 and 12 of Figure l, it is seen that the direct current component dE is dependent upon the amplitude, width and repetition rate of the pulses. The amplitude of the pulses, of course, is dependent upon the color valuesof the television image. It has been found that by properly controlling the time duration or width of the pulses occurring at a particular frequency, the direct current component dE may be made of such a value that the sine wave 13 always hasv a substantially zero value at the green and red sampling times G and R and a maximum value at the blue sampling times B.

By fixing the width of the pulses at such a value, variations in the pulse amplitude in accordance with the picture values effect variations in the direct current component and the amplitude of the sinusoidal component so that, irrespective of instantaneous pulse amplitude, the blue video signal sine wave always has a substantially zero value at the green and red sampling times. Figure 1 illustrates that the pulses 12 are of somewhat lower amplitude than the pulses 11. The direct current component represented at dE, accordingly, is smaller in magnitude than the direct current component dE of the pulses 11. Similarly, the sine wave 13 has a smaller amplitude and a direct current component of suitable value to insure that the wave has zero values at the green and red sampling times.

In Figure 2, another extreme condition is analyzed. It is assumed that the television picture includes blue, green and red color components which are all of equal intensities, varying similarly in different parts of the picture. These conditions are typical for black and white television systems. Blue, green and red pulses 14, 15 and 16, respectively, are shown of relatively large amplitude and blue, green and red pulses 17, 18 and 19 are of somewhat smaller amplitude. In a manner similar to that described with reference to Figure l, the direct current component of each series of color pulses is represented at dE for the large amplitude pulses and at dE for the smaller amplitude pulses. It is seen that the fundamental frequency of all of the pulses combined is three times that of the pulses for a single color. Also, since the low pass filter is designed to attenuate all frequencies materially higher than the fundamental frequency at which a single color video signal is sampled, it is seen that the alternating current component of the wave 21 derived from the filter output will be zero. However, there will be present in the filter output circuit a direct current component which has three times the magnitude of the direct current component due to any one series of pulses representing a single color. The direct current component derived from the iilter is indicated in Figure 2 as equal to 3dB for the large amplitude pulses and 3dB for the small amplitude pulses.

It is seen that, when the wave 21 is sampled at a receiver, the samples for the various colors will be of equal amplitude which is comparable to operation in a black and white system. ln other words, the direct current component represented by the curve 21 varies in amplitude in accordance with the signal modulation, thereby enabling production of a conventional black and white image.

In order to more completely understand the operation of the present system in effecting good cross talk balance, reference now will be made to Figure 3. A condition intermediate of the previously described limiting con# ditions is assumed, such as when one of the colors is completely lacking in the picture. Figure 3 will be described on the assumption that blue is lacking in the television picture.l The pulses 22 and 23 represent the green samples at relativelyvhigh light intensity. The pulses 24 and 25 represent the red samples at a high light level. Similarly, the pulses 26-27 and 28-29 represent, respectively, green and red samples at a somewhat lower light intensity. As in the previously described Figures 1 and 2, the direct current component resulting from a single series of either the red or green pulses is represented at dE for the high level pulses and at dE for the low level pulses.

After passing these pulses through the low pass lter, there is derived from the output circuit of the filter a sinusoidal wave 31. This wave varies in amplitude in accordance with the amplitude of the pulses from which it is developed. The direct current component of the wave 31 also will be noted to be substantially equal to twice the direct current component of a single one of the groups of pulses. It is to be especially noted in this figure that the wave 31 is shifted in phase in such a manner that the green and red samples and the corresponding instantaneous amplitudes of the composite video signal wave 31 are displaced equally on different sides of each of the positive peaks. Accordingly, they are substantially equal in voltage amplitude. Furthermore, it will be noted that the amplitude of the wave 31 is zero at the blue samplingl times. Consequently, it will be seen that, when the wave 31 is sampled at the receiver, there will be derived therefrom substantially equal green and red samples and nothing will be derived therefrom representative of the blue component.

-lt will be appreciated that, in actual practice, many different modications of these typical examples chosen for purposes of illustration will be produced. However, it will be understood that all possible arrangements adhere to the same underlying principles of operation. To illustrate just one additional arrangement, reference will be made to Figure 4. It is assumed that, in a particular portion of the picture, there is considerable green, a moderate amount of red and a small amount of blue color present. The pulses 34, 35 and 36 represent the green samples, the pulses 37, 38 and 39, thered and the pulses 41, 42 and 43 represent the blue samples. After passing these different color signal samples through the low pass filter, there is derived a composite video signal wave 44. It will be understood that this composite wave 44 consists respectively of green, red and blue waves 45, 46 and 47.

ln view of the foregoing description, it is seen that the direct current component of the green video signal wave 45 is represented at dEG. In a similar manner, the

- direct current component of the red video wave 46 is represented at dER, and dEB represents the direct current component of the blue wave 47. An inspection of the waves 45, 46 and 47 shows the manner in which the proper selection of the direct current component of these waves enables the system to effect a good cross talk balance. For example, it may be seen that, at any of the green sampling times, the green wave 45 has a maximum amplitude. At the same time, the red and blue waves 46 and 47 have Zero amplitudes. The same conditions exist at any of the red and blue sampling times.

From the foregoing analysis, it will be seen that, by making the sampling pulses of relatively short time duration, by properly timing them relative to the composite video signal wave, and by converting them to a fundamental frequency sine wave, automatic cross talk balance or rejection is obtained. For a given repetition rate of the sampling pulses, it is necessary that the width or time duration thereof be suitably adjusted to give the desired direct current component to the sinusoidal waves of the video signal. The-sinewave which is developed-attire. filter output is seen: tohavel the same-peak-to-peakampli# tude irrespective ofv whether oneror two pulses of 'equal amplitude vare applied to 'the filter input. circuit; The' direct current component varies directly with the number of pulses. Itr also is seen=thatthephasing or timing of the sine wave which is developed from two series of pulsesis changed with respect to that developedffrom one series of pulses.

\While it may appear from theforegoinganalysis that ct'aniplete cross` talk rejection maybe lobtained cnlyinstantaneously at'times when thelwaveto bef sampled has aipeak lvalue and the'other waves have Izero amplitudes, it is to be understood that successful sampling'of such arfvideo-signal wave at a receiver rnayV be effected by takingfsamples of 1a magnitude as great asl 30 degrees at the sampling frequency.

Byireferring now to Figure 5'of the drawings it will be shown that samples of this magnitude are capable of producing substantially undiluted'color signals. In Figure 5, there are reproduced portions of they green, red and blue waves 45, 46 and 47, respectively, of Figure 4, as described, these wavesare the components of the cornposite wave 44. It is assumedthat av green sample is to be extracted from the wave 44. The width of the sample, in accordance with presently preferred practice, is approximately 30 electrical degrees at the sampling frequency. The green sample is represented by the' hatched area 48 under the curve 45. It will be seen that, during the green sampling time, the red video signal wave 46 is changing from a relatively small negative value through zero to a positive value. Consequently, a sample is taken of this wave. It will be seen, however, that the sample consists of a negative portion 49 and a positive portion 51. Except for small deviations in the shape ofthe wave 46 in this region below and above the zero line, it will be seen that the negative and positive portions 49-and 51, respectively, are substantially equal and'electively balance one another so that the net effect is substantially zero. Likewise, it will be seen that, during the green sampling time, the blue video signal wave 47 also is sampled. Consequently, there are produced positive and negative samples 52 and'53, respectively, which are of substantially equal magnitude, thereby balancing one another to produce a'zero net effect.

Referring now to Figure 6 of the drawings, there is shown color television video signal-generating andrtransmitting apparatus embodying one of the features of this invention. Differently colored light which is retiected from an object 54 is projected by a suitable optical system represented by the lens 55 upon the color television camera equipment. The light from the object is separated into its primary component colors by suitable means such asblue, green'and'red filters 56, 57 and 58. The light which is permitted to pass through each ofthe filters is directed onto the photosensitive electrodes of theiblueygreen and red camera tubes 59, 60 and 61 respectively. These tubes may be conventional camera tubes such as image-orthieons or the like. In any case, they must' be capable of response to the differently colored light projected respectively thereon.

The video signals derived from the respective'camera tubes are representative ofthe blue, green and red componentsof the television subject. These video signals are'developedy substantially concurrently. In order that they may be transmitted on a time division multiplex basis in accordance with the system disclosed in the copending Evans application referred to, there are provided blue, green and red gate4 amplifiers 62, 63 and 64 respectively. These devices-function to sample the differently colored'video-signals derivedfrom the camera tubes. The-gate' amplifiers preferably all are'of the same character. Accordingly, lthe details of only the blue Vga-te amplifier? 62 fare shown and `described herein; It will bef understood thattheigreeni and redgate amplifiers 63 and 64E-may he substantially-identical tothe blue gate amplifier1 The sequential: operation of the gate amplifiers is controlled-bya wave` derived from a sampling frequency oscillatorS. This oscillator may be any conventional apparatus for producing a relativelyl high frequency sine wave. Its essential requirements are that it be stable in itsfoutput frequency and also-subject to control-by means of periodic pulses. A typical form of oscillator suitable for this purpose is shown in the book entitled Wave Forms, published by McGraw-Hill Book Co., Inc., at page 143, with particular reference to Figure 4-45. The frequency of the oscillator 65 is controlled by conventional synchronizing circuit and deflection generating apparatus 66. The particular means4 of such control forms no part of the invention. As disclosed in the copending Evans application referred to the control pulses for the oscillator65 may be the horizontal or line synchronizing pulses. Alternatively, a short burst of alternating currentz at the sampling frequency occurring during the horizontal-blanking periods may be used for this control. 'Ihislatter type of control system is disclosed in a copending U. S. application of A. V. Bedford, Serial No. 143,800, filed February l1, 1950, and titled' Synchronizing Apparatus, now Patent No. 2,728,812,v granted December 27, 1955.

The sinusoidal output wave derived from the oscillator 65-is impressed' at 120 electrical degree intervals upon the-blue, green and red gate amplifiers 62, 63 and 64 respectively. The different phase relationships are determined by delay network formed of a pair of serially connectedtransmissionlines 67 and 68. One terminal of the network is coupled to the oscillator 65 by a capacitor 69. The'other terminal of the network is connected to ground through a resistor 70 having a value equal substantially to the characteristic impedance of the transmission lines. By this means, reflections in a reverse direction over the lines 67 and 68 are prevented. The ungrounded terminal of the delay network is coupled to the blue gate amplifier 62. Each of the lines 67 and 68has a length sufcient to produce a time delay or phase change of substantially 12() electrical degrees at the samplingfrequency. Accordingly, the junction point between the lines is coupledv to the green gate amplifier 63, thereby delaying its operation by degrees relative to the operating'time of the blue gate amplifier 62. Similarly, the remote or grounded terminal of the delay network iscoupled to the red gate amplifier 64. Hence, its operation is delayed 120 degrees relative to the operating time ofthe green-gate amplifier 63 or 240 degrees relative to the operating time of the blue gate amplifier 62.

The output circuits of the blue, green and red gate amplifiers 62, 63' and 64 are connected together as shown and to a sourceY ofk positive voltage indicated at- -i-B through a load resistor 71. The combined output circuits of the gate `amplifiers are coupled to a signal adder stage72. The output circuit of the adder is coupled to a low pass filter 73 capable of attenuating all frequencies substantially higher than the fundamental of the sampling frequency. The output of the low pass filter is coupled to a conventional television signal transmitter 74 for the development of a composite television signal by which to modulate a carrier wave which in turn may be radiated by an antenna '75.

The 'synchronizing circuit and de'ection generating equipment`66 is coupled to the television signal transmitter 74 as shown in a conventional manner for the usual development ofthe composite television signal. The deflection generating apparatus also is coupled to the deection apparatus associatedl with the camera tubes 59,'6f`andi61'. In this manner, the scanning operation of the three camera tubes may be concurrently controlled.

The blue video signals derived from the camera tube 591 are impressed upon the blue gate amplifier electron tube 761by meansofacouplingwhich includesa capacitor 77 andafgrid leak resistor 78. The tube 76 normally is biased'to `a non-conducting state. This tube is controlled by a driver electron tibe 79. The in-phase sampling frequency oscillation derived from the oscillator 65 is coupled to the control grid of the driver tube 79 by a capacitor 80 with which is associated a grid leak resistor 81. Preferably, this resistor is made adjustable as shown. The cathode of the tube is directly grounded. The output circuit of the tube derived from the anode thereof includes a resistor S2 and a series-connected inductor or coil 83 coupled to a source of positive voltage indicated as '-l-B. The coil 83 functions to suitably shape the Vform of `the pulses developed at the anode of the driver tube 79. f

The `anode of the driver tube is coupled by a capacitor 84 to the cathode'of the gate tube 76. The cathode of this tube is grounded through a resistor 36 and also is coupled to a suitable source of positive voltage such as indicated `at `-l-B through a resistor 87. By this means the tube 76 is biased so that normally it is non-conductive.

Normally, `the tube 79 also is biased to its non-conducting state. The tube 79 is rendered conducting periodically by pulses derived from the sampling frequency oscillator 65. Accordingly, pulses of negative polarity are developedl at the anode of this tube and are impressed upon the cathode of the gate tube 76. This tube, accordingly, is rendered conducting for a short interval of time to reproduce in `its anode or output circuit afsi'gnal corresponding to the blue video signal derived from the camera tube 59 at that time. of the pulses developed in the output circuit of the gate tube 76 depends upon the amplitude of the video signal as previously described.

The width of the pulse developed in the output circuit of the tube 76` may be varied by a suitable adjustment of the driver tube grid leak resistor S1. By this means, the direct current component of the blue video signal samples may be properly set for effective cross talk balancing purposes as previously described.

Inasmuch as no two of the gate amplifiers 62, 63 and 64 are operative at the same time, the output circuits thereof may be combined through a common load impedance such as the resistor 71. Accordingly, there will betdeveloped across this resistor three series of pulses derived respectively from the three gate amplifiers. These three series of pulses, which may correspond to the pulses shown in Figure 4, are impressed upon the adder apparatus 72.

This apparatus consists essentially of an electron tube 88 having a control grid which is coupled by a capacitor 89 `to the combined output circuit of the gate amplifiers. A grid leak resistor 90 is included in the coupling circuit. The cathode of the tube is connected to ground through a self-biasing network including a resistor 91 and a bypass capacitor 92. Preferably, the capacitor 92 is made Variable. By such means, the amplification of the video signal samples may be adjusted to provide` the desired relationship to the direct current components as previously described. Space current for the tube S8 is derived from a suitable power supply indicated as -l-B which is connected to the anode of the tube through a load resistor 93. The video signal adder 72 functions to amplify the combined outputs of the gate amplifiers 62, 63 and 64 and also serves as a buffer stage between the low pass ilter and the gate amplifiers.

The low pass filter 73 functions as described to convert the pulse samples into substantially sinusoidal Waves at the sampling frequency. These component Waves then are combined into a composite wave by which a carrier Wave is modulated.

Having in mind the described character of the video signal' waveforms of an elemental multiplex color television system, reference now will be made to Figure 7 of the drawings. The circuit diagram is that of a color television image .reproducing system with typicalcircuit The amplitude components of the sampling system in accordance with the present invention shown in detail. color television signal which is intercepted by an antenna 94 is impressed upon a television signal receiver 95. It will be understood that this receiver includes conventional apparatus such as a radio frequency amplifier, a frequency converter or first detector, an intermediate frequency amplifier and a second or signal detector.

The signals derived from the output of the receiver 95 are impressed upon each of two channels. The composite video and blanking signals are impressed upon a video signal amplifier 96. The video signal amplifying channel also includes an output or driver stage 97 which is coupled to the amplifier 96 by a keyed clamping circuit 98. It will be understood that the clamping circuit 98 is illustrative only. Any other conventional direct current reinsertion arrangement may be used, if desired. The output of the video driver stage 97 is coupled to the beam intensity control grids of blue, green and red kinescopes 99, 100 and 101 respectively. By means of such a circuit arrangement, it is seen that the complete video signal wave is continuously impressed upon one of the electron beam intensity control electrodes of the electron guns of the three color kinescopes.

The television synchronizing signal is impressed upon conventional synchronizing circuit and deection generators 102. It will be understood that this apparatus includes means for separating the horizontal and vertical synchronizing pulses and also saw-tooth energy generators for energizing the deflection systems of the kinescopes. Color synchronizing signals, such as disclosed in either the copending application of Evans or that of Barton previously referred to, also are derived from the synchronizing apparatus 102 at the horizontal synchronizing frequency. These signals are impressed upon a sampling frequency oscillator 103 to maintain it in synchronism and proper phase with the received signals. This oscillator may be conventional apparatus for producing a relatively high frequency sine wave. Its essential requirements are that it be stable and :also subject to control by means of the color synchronizing signals. Accordingly, it may be substantially identical to the sampling frequency oscillator 65 of the transmitter shown in Figure 6.

The sinusoidal voltage at the sampling frequency derived from the oscillator 103 is impressed upon an amplier 104 used as a driver for the color keyers. The sinusoidal voltage derived from the output of the driver 104 is impressed without phase displacement upon a blue color keyer 105. This voltage also is impressed upon one terminal of a pair of serially connected delay lines 106 and 107. Each of these lines is effective to produce a delay of substantially electrical degrees at the sampling frequency. At the junction point between the lines 106 and 107 a connection is made to a green color keyer 108. A similar connection is made to a red color keyer 109 at the terminal of the line 107. This line terminal also is connected through a resistor 111 to ground,

thereby terminating the lines in their characteristic im-` pedance. In this way, reflections in a reverse direction over the lines are prevented. The green and red keyers 108 and 109 preferably are similar to the blue keyer 105.

The output of the blue color keyer 107 is coupled to the electron gun cathode of the blue kinescope 99. In a similar manner, the output of the green and red keyers 108 and 109 are coupled respectively to the electron gun cathodes of the green and red kinescopes 100 and 101.

The partial color images reproduced upon the luminescent screens of the kinescopes may be combined optically in any desired manner. For example, as shown herein, a pair'of suitable dichroic mirrors 112 and 113 may be lemployed to direct the three color images upon the undersurface of a reflecting member 114 which may be viewed The composite directly. The inventionis Vnot limited to this, particular type-.ofl reproducingk apparatus. ASingle multicolor kinescopesffmay bev usedas'V more fully. disclosed hereinafter.

"Beforevdescribing-some' of-the circuit details vof this embodimentof the invention a brietdescriptiou of its general mode ot operationwillbe given. Normally, the cathodes'f-off-the color kinescopes` 99, 100 'and-101mm biased positively relative to groundl so that;- irrespective ot the.L videosignal'.- voltages yimpressed. upon the control grids thereohi-the electron! guns are eiectively inoperative to produce' electron beams. The biasing of these cathodes is=.ove'rcome ina predeterminedrsequence'which, in the illustrated example, is blue, greenand red. :'Accordingly,

atlthe timethat the blue video signal .component of; lthe compositerwaveis impressed 'upon the kinescope control gridsythe'biasing-of the cathode of theblue-kinescope 99'li's overcome Vso that an electron beam is Iproduced to exciteuthewluminescent screen. The magnitude of this excitation is' determined by the amplitude ofthe video signal impressed upon `the control grid.

At .the'uext succeeding instant, when the received video signaiwave represents the green componentof the image, the cathode: of lthe green kinescope 100 is conditioned to render the electron beam effective `to eXcitethe'luminescentscreen. lnasimilar manner, the` cathode of the red kinescopewv 101 is` keyed concurrently with the impression uponl'the kinescc-pe control-g-ridsuof that'portion of the video: signalwave-which represents the redi color cornponent.

'The clamping-circuit 98,. shown principallyas an example, is akeyed clamp of thetype covered by U.'S. Patent 2,299,945, issued October 27, 1942, to KarlV R. Wendt and titled Direct CurrentReinstating Circuit. Briefly, it consists of -a'storage capacitor 115 connected in series between the output*A of the video signal amplifier 96 and thedriver-stage'97. A shunt circuit toground-includes aafparallel arrangement ofinverted diodes v116 and 117 having 4respectively in `series therewith substantially equal resistors 118- and 119.

Normally, the diodes are non-conducting. Consequently, there is an open circuit between fthe capacitor 1,15T and-ground. Hence, the capacitor remains charged to'fwhatever ypotential'l :is` last` impressed thereon. Periodically, substantially in synchronism with the lhorizontal synchronizing pulses, a positive pulse such as shown-at 12'1f"is1.'rnp`resse'd-*upon the anode of the 'diode-116 by a capacitor v122 coupling the diode. to they synchronizing circuit 102. Atthe same.' time, a negative vimpulse such asshown at 123"is|fimpressed upon the 'cathode of` the diode- 117by a.v capacitor 124'coupling theldiode tothe synchronizingci-rcuits 102. Keyed: vin .this manner, the diodes are couditionedfto provide a low impedance circuit toi'grou-nd from the capacitor 115 vpermitting the charge on' the 'capacitor to change in:v` accordancev with theA video signali information received' at that. time. ThisV is.a'well known 'expedient 'inr television systemsforetfecting-backgfrouridlcontrolor direct current reinsertion. As `previouslylindicated, otherftypes of direct current reinsertion appara-tus.'may4 be used without= materially'changing the operation of the system.

The videoampliier driver stage 97 is quiteiconventional. It consists of an electron tube'125, Which, in thiscase, is a pentode. The control grid 126 is directly coupled tofthev 'clamping-circuit98. Thescreen gridi127 is supplied withf=a' positive potential by means ofa resistor'v 128 connected' -to' a source of positive voltagefindicated'at 42B'. 'I-hev screen gridisbypassed to ground by a capacitor 129. Also, the'` suppressor'grid 131 is grounded. :The cathode ofrftheutubefis connected to ground throughI a'protective res'istor'132. The: anode ofl the-:tube is coupledl to the sourcejof space'current indicated at -ieBsthroughrconventional: peaking.'circuits.r including-fa coil 133.-"shunted by a'rjesis'tora13.4,v a series 'resistor' 135,2 and awsecond' coil-136. Theffoutputf from-the video'- amplier driver stage-'97 i is 112 derived from the vjunction point between thehighpeaking coil133 and resistor 135. As shown,.this point is coupled to the control grids of the electronv guns-ofv the blue, green and red kinescopes 99, and 101.

The sampling frequency driver 104 includes an electron tube 137 which, as shown, may be a pentode. The cathode is connected to ground through a resistor 138 bypassed by a capacitorr139 for self-biasing operation ina well known manner. The sampling frequency voltage derived fromfthe oscillator 103 is impressed upon the control grid'141 by a coupling capacitor 142 with .whichisassociated a grid resistor 143. The screen grid 144 has impressed thereon a suitablepositive potential by -means of a resistor 145 connected to a voltage source indicated at +B. The screenl grid also is bypassed to ground by a capacitor 146. The suppressor grid 147 is conventionally grounded. Space current for the tube is provided by-'a connection of the anode to the'sourceA indicated at--l-B through a coil 148. A capacitor149 coupled betweenthe anode of the tube and ground is associated withl the coil 148 in order to tune the output circuit of the -tubeto the frequency of ther oscillations derived from the oscillator The 4output circuit ofthe driver 104 is derived from the anode of -the tube 137 and is coupled by acapacitor.151 to the color keyers as described. `The tube 137 normally is grid-leak biased by means of grid current, which-'is stored' iny capacitor 142, leaking oli through resistor 143 during the time intervals between successive positive peaks ofthe sinusoidal voltage derived from the samplingtrequency oscillator 103.

inasmuch as all o fthe color keyersare similar, the details of the blue color keyer only havebeen shown. This devicev includes an electron tube 152 of the pentode type. The sinusoidal sampling voltage is impressed upon. .the control grid 153 by a coupling capacitor; 154, a grid leak resistor 155 and a grid current limiting resistor 156. The cathode of the tube is connected to groundthrough a selfbiasing network including a resistor 157 bypassed by a capacitor 158. vThe screen grid 159 is connected to a source of-positive voltage indicated at `-l-B through a vresistor 161 and is bypassed to ground byfa capacitor 162. Also, the suppressor grid 163v is grounded. Spacelcurreut for the tube is derived` from they source indicatedV at f-l-B'whichis shown connected to the anode. of the tube through a series resistor-164and coil 165. The anode of. the tube also is coupled to the cathode 'ofv the blue kinescope A99 by-a capacitor 166.

'The colorrkeyer tubes, such as the tubef152, also are grid-'leak biased? by drawing' grid currentonrthepeaks of the sinusoidal sampling frequency voltage-impressed thereon. --By'suitable choice of. circuit parameters, the biasing of the .tubesis controlled sothatthey arev made conducting onlyat the positive peaks of the sampling: frequency voltage for time -intervals equal substantially to the sampling periods.

Normally, the cathode of the blueikinescope 99` is biased sufiiciently'positive to completely interrupt the electron'bearn of this tube. This positive biasingf the kinescope-c'a'thode is effected by a`circuitvwhich1includesra series `resistor167' connectingthekinescope` cathodefto a tap on'apotentiometer168. 'Theterminals'of the potentiometer are connected respectivelyto'the positive voltage' sourceY -l-B-and.l ground. This biasingrcircuitis vbypassed to ground by capacitor 169.

Normally, the: tube 152 Iofthebluelcolor keyer=.is in a minimum conducting or` completely non-conducting state. Insuch' a condition,.the positive'potenti'al derived fromthe' potentiometers168 isaeective to biastlie cathode of the blue kinescope 99 so that the electrony beam-is completely cut. ol. -ln response lto a sampling frequency pulse derived fromy the -driver 104, 'the'. keyingl tube 152 becomes' conducting. The control voltage developedmt theanode. ot this tube, therefore, is. a short-. negative-polaritygpulse. Whenfsucha pulse is impressed upon'ihe 13 cathode of the blue kinescope 99 by the coupling capacitor 166, the normal positive biasing of the electron gun of this kinescope is overcome. In this manner the electron beam is keyed on to excite the luminescent screen of the kinescope. By suitable adjustment of the circuit parameters, this event may be made to coincide with the impression of the blue video signal upon the intensity control grid of the blue kinescope 99.

In a substantially similar manner the green and red color keyers 108 and 109, respectively, function to control the electron beams of the green and red kinescopes 109 and 101, respectively.

With reference to a feature of this invention which will be described subsequently in conjunction with Figure 8 of the drawings, particular attention should be given to the space current connections for the electron tubes 137 and 152 of the apparatus of Figure 7, It will be understood that similar circuit connections are provided for the green and red color keyers 108 and 109. The anode circuits of all of the electron tubes are connected through relatively low impedance conductors to the positive terminal of the. source of space current. By reason of such circuit connections, the apparatus operates substantially in the manner described.

By referring now to Figure 8, there Will be described a feature of this invention by which the sampling system may be converted automatically from black and white to color operation and vice versa. The particular feature of this invention by which such a result is achieved is embodied in the color keyers and the tuned amplifier driver stage therefor. Accordingly, there is shown only one of the color keyers and the `driver stage. It will be understood that the other color keyers (not shown) will be substantially identical to that shown. The driver stage 1614i: is identical to the driver 104 of Figure 7 except for the screen grid and anode connections of the tube 137. The screen grid 144 is connected to the positive voltage source +B through a resistor 145 as in the form of the invention shown in Figure 7. Similarly, the screen grid 159 of the blue color keyer tube 152 is connected to -l-B through a resistor 161. It is to be especially noted that each of the screen grids is connected through individual resistors to the source of positive voltage.

The anode of the driver tube 137 is connected through the coil 148 to a common anode bus bar 171. The tuning capacitor 149 is connected, in this case, between the anode of the tube 137 and the positive terminal of the `voltage source indicated at +B.

In a like manner, the anode of the blue keyer tube 152 is connected through resistor 164 and the coil 165 to the bus bar 171. The kinescope bias-adjusting bleeder potentiometer 168 also is connected to the common bus bar 171. This bus bar is connected to the positive terminal of the voltage source indicated at .+B through a common voltage-dropping resistor 172.

As long as sinusoidal oscillations at the sampling frequency are impressed upon the driver tube 137, this device and the color keyers operate substantially in the manner described. The driver tube 137 and the color keyer tubes such as the tube 152 are grid-leak biased as in the preceding case. The time constants of the gridbiasing circuits are of such a character that suitable negative biasing voltages are maintained at the control grids of the tubes to maintain the tubes non-conducting between the times of impression thereon of the sampling frequency impulses.

Should the sampling frequency oscillations be discontinued for any reason, the grid-biasing facilities for the electron tubes would be inelfective to maintain the tubes nonconducting. Consequently, each of the tubes will draw more space current. Since the total space current for all of the tubes traverses the common resistor 172, it is seen that the result of the additional currentconduction of the tubes is to decrease the positive potential of the bus bar 171. It is assumed that the setting of the potentiometer 168 by which thenormal cathode biasing voltage for the color kinescopes is adjusted is not changed. Accordingly, it is seen that, as a result of the decreased positive voltage impressed upon the bus bar 171, the positive cathode-biasing of the color kinescopes is reduced. By suitably choosing the value of the resistor 172, the bias on the three kinescope electron guns may be automatic/ally reduced to the Value required for black and white unsampled operation. Such a result is produced simply by interrupting the sampling frequency oscillations. The cathode resistors of the electron tubes prevent overloading of the associated tubes when the sampling frequency oscillations are interrupted.

. A feature of such a character is useful in designing television receivers for reproducing images either in color from a sampled video signal wave or in black and white from an unsampled video signal wave depending upon the selected channel.

As illustrative of the fact that the invention is not limited to any particular type of image-reproducing apparatus, reference now will be made to Figure 9. The image-reproducing apparatus shown in this ligure is a single cathode ray tube capable of reproducing an image in a plurality of component colors. of tube shown is that disclosed in greater detail in a copending U. S. application of A. C. Schroeder, Serial No. 730,637, tiled February 24, 1947, and titled Picture Reproducing Apparatus, now Patent No. 2,595,548, granted May 6, 1952.

The cathode ray tube 173 is provided with a plurality of electron guns in order to produce a like plurality of electron beams by which to excite the luminescent screen. If it be assumed that a tube of this type is to be used in a three-color television system, three electron guns will be provided. The three electron guns include cathodes 174, 175 and 176. Associated respectively with these cathodes are beam intensity control grids 177, 178 and 179. It will be understood that, as shown in this gure, the electron guns are merely diagrammatically represented. Actually, as disclosed in the Schroeder application referred to, the three electron guns are mounted symmetrically, at substantially degree angles relative to one another, about the central axis of the tube.

The tube 173 also includes an apertured electrode 181 and a luminescent screen 182. The luminescent screen is made up of a multiplicity of phosphor areas of subelemental dimensions. The sub-elemental phosphor areas preferably are arranged in groups of three. Each group is associated with one of the apertures in the electrode 181. The phosphors of the respective sub-elemental areas are capable respectively of producing light of the cornponent image colors when excited by an electron beam. The particular phosphor area which is excited is determined by the angle at which the electron beam traverses the aperture of the electrode 181. This angle, of course, is determined by the particular one of the electron guns which is energized. It is seen, therefore, that to effect the reproduction of an image in its component colors, by means of a tube of this type, it merely is necessary to key the electron guns of the tube in a predetermined sequence and in synchronization with the reception of the correspondingly colored video signal.

Accordingly, as indicated in this figure, the control grids 177, 178 and 179 are coupled to the video signal channel in substantially the same manner as the control grids of the kinescopes shown in Figure 7 are coupled thereto. By this means the composite video signal wave is continuously impressed upon the control grids of all of the electron guns. The cathodes 174, and 176 of the electron guns are coupled respectively to blue, green and red keyers. These connections may be made in any suitable manner, such as indicated in Figures 7 or 8. In view of the foregoing description of the manner in whichthe receivingl apparatus of Figures 7 and,8 operates, it is considered unnecessary to describe further In general, the type 15, the,` .operation .of ,the systemrwhemusing ,a single multi-k colontubesuchlasshown in Fi'g'ure 9.

It.. is'. to 4.be furtherunderstood that .the y.present inventionnnayfbe employed. 'successfully Awithlother multicolor kinescopesprovided either witha plurality offelectron, 5 guns orwithla singleelectron gun..4 For example, another` type yof multicolor kinescope with vwhich the invention maybe usednand which has ,a plurality of electron guns is disclosedtimUJ S. Patent2,481,839,' grantedrtoALN. Goldsmithon ,September l3,"l949, and .titled Color Tele'- 10 visioni.

Atypical example, ofa multicolor kinescope having..

a single electrongun, with -whiehnthe present invention may, berusedis disclosed in.U.S.' Patent No. 2,446,791 granted ,to..A-.C. Schroederon.. Agust 10," 1948,",and, titledfColor Television, T'ubef In the kinescope covered,` by,the.Schr.oeder:.,patent referred to, color separation is elected by selectively deflecting a sing-leelectron beam over,.a luminescent screenshaving theidifrent color-producing@ phosphors arrangedr thereon in. subele'mental 20 stripsrextendingasubstantially the. entire ,Width of 4'the screen. t

ThepreSent invention :alsonis vparticularly adapted 4for use .witha multicolor kinescope ,employing l,a singleV ele`ctrongunofytheqtype.,disclosedntcopendijig U. Sfapplica-r Y tiontof .Rt Law,.Serial No.. 165,552Q1'ed. Iu'ne ,1; 1950,' and vtitled,.Color, Televisioni" Thev general principle;` uponowhich-this tube operates is somewhatsimilr to' that of the apparatus disclosed in the copending ,Schroeder` application 4referredio.. The color reproduction` is ef' 30- fectedby ,the angle atvwhich the .beam'fapproaches the. targetelectroder However,l insteadof; having three .ele"c. tron beams,` as in the device covered bythe Schroeder.. application, the ,Laws apparatus ,employstfarsingle ele'ce trontbeam. 1n order.to varypth'eVangleof-'approach'to 354 the electrode thesingle' .electron .beam.-has imparted theretoatspinning ftype of motion before itis deected overthe luminescentgscreen. Abeamlof 'thistype ,may be `keyed sothat itis rendered 'eiective at th'e proper times-,to approachfthe-target electrode from the angle 40 necessary lto produce light of th desired icol'or.VV Theibeam keyingis made to "coincid'e/withthe video signalreceived at that timea From the foregoing` description off'an, illustrative 'embodinentof the. invention, itl-maybe seen that there is provided "an improved time division multiplex system especiallyadapted fo'r colortelevision. One of 'the im. provements l17in accordance with. this invention .is th means sfo'r developing thee composite'- video signal. Wave so that.'eife"ctive ,crosstalk balance is` automatically rl` 50 achieved bythe' ,relativelyl simple" expedientl Iofproperly'l choosinghthe width' or time duration of the videosignal samples. In addition,` the sampli'r1`g. circuits'1atthe re-v ceiver have been improvedby simplificationl Tle nature of th'e invention may be determined from .55 the foregoingfdis'closure of "an .illustrativeembodiment L thereof;Y scope of fthe invention is defined in .the appended claims;

What'is claimed is:

1.` Av color television system comprising` means for gen-V 60 erating ,concurrently .individual videorsignals representa' tive respeetivelyfof the component'colors ofan imager. means for deriving discrete' samplesfromsaid individual video :signals in qsuccession',A 'means.,for convertingjsaid discrete signal "samples into a .composite video. signalf wavefmeans controlling the time duration of saidfs'igill samplesV to produce successive 'instantaneous amplitudes :f of vsaid composite video" signalwave' representative respectivelyl'ofon'e only of said'l'lndividual video signals'fat a ytime;cathode ray' apparatus includiga cathode" and a 70 gmd Vfor'-repr'oducir1gsaid'- vimage in' its Acomponent colo'rs, means' for continuouslyt'impressing [said "received com- "y posite video ysignal 'wave `uporrrsaid grid, andf'mea'ns., coupled "tosaid fcatho'deto Tintermittently operate said L cathode Lray 'apparatus concurrentlyl witlil the reception 75 lit-3r of said instantaneous amplitudes of said composite video signalwave.

2' A^vk color `4television syste'rnV comprising,I meansl for" generating concurrentlyl individual videosignals repre= sentatve'respectively of the component colors ofan image", means forderving relatively nsrnall discrete samples Vfrom said individual video signals `in succession; meansA forwconvertingsaid discrete signal samples into a composite video signal Wave, means controlling the vtime durationofsaid video'signal samples toI produce successive' instantaneous amplitudes of said composite -video signal wave representative-respectively of'one onlyof said video signals at a time, meansv for transmitting and receiving said composite video signal Wave; cathode ray apparatus "for" reproducing said image in its`componentb colors, electron beam-developing'means including a cath-y ode and fa control grid, 'means for continuously impressingsaid received compositevideo signal wave upon said control grid, and means vcoupled 'to said cathode-to keyl said"beamdeveloping means 4for operation concurrently withthe reception' of :said instantaneous amplitudes of said composite video-signal Wave.

3:: A color televisionsystemcomprising,- means for generatingconcurrently 'individual' -video signals representative respectively of the component-"colorsof an image, means forderiving'relatively small discrete samples from saidindividual video signals in succession, means for converting-'said discrete signal; samples into individual continuous Awaves,'means controlling the time `duration of said individual vide'o signal samples to producemaxi-v mum""amplitude's'ofieachof said- Waves concurrently with' substantially Zero `amplitudes ofthe others' of 'said Waves, means--for"transmitting;and'receivingsaid Waves as a composite'video "signall Wave; cathode rayy apparatus for, reproducing `said image' initsv component/colors, electron beam-developing m'eansineluding "a cathode'and a ibeam intensity-lcontrol grid'gmeans for continuously impressing said-2receivedcompositevideo'signal Waveupon said conL trol'grid, fandmeans-coupled to said cathode to key said beam-developing `means Lfor operation Iconcurrently with theV reception'sof the maximum Iamplitudes 4of said ini dividualf'video signalwaves.

4xv In` a color television system',- apparatus 4for developing a composite time-division multiplexsignal wave rep. resentatiivef-of'fthe'' coloncomponentsof t successive elementalfareas of-an image-comprising means for generat-' ingf-:concurrentlyl IindividualH video signals representative" respectivelyofifth"componentHimagecolors,l sampling means having an output for 'each 'osaid videosignals* operative/fsuccessively" at a predetermined video t signal samplingi-frequency for producingffsamples of saidvideo* signals aalowfpass'filtercoupled 'to ther-outputs of said` sampling means f andflhaving-y a cuto' frequency substan tially 'equaltoi-'said isampling frequency, -and'` means coupledutov1vsa'id sampling means yto control@ the' operative periods of said sampling 1'means suitably' to" produce xat saidtflteri! outputa :Wave-y fo'r- Y'each component image color havinga directcurrent'component ofy such a magniv tude'. relative lto2 the; pealC-tolpeak"y amplitude? that -its m'axi# mumi-lvalu'e occurs;.substantially"simultaneously with? thee occurrence oflfzerowalues-oftheothers'fofsaid'lwavess 5 i tInaa icolor'televis'ion-system, apparatus vfo1-develo"pL ingvarzcomposi'te time division multipleX signal-wave rep# t resentativefof. the 'colori components of-J'Successiveeleaf' mentalnareasfzofIan image, 'comprisin'gmeans for -gen"- eratingfco'ncurrentlyf,individuali video signals representa? tive respectively of the component image-colors, samplingl meansthlavinggan-outputor' each of saidvideosigna'ls operative succ'essivelyat `120degree intervals at a prede-5 terminedttvide'o'signalsampling 4frequency for .producing pulse' samplesr'of"saidfvideolisignals,'a low vpassiil'ter` coupled"'to`the outputsof'said sampling means and havinga cutoifrequencysubstantially equal tosaid'sampling f, frequency,` and means coupled to said sampling means .to .Control 'thlengthllofsaid pulse samples suitablyto produce at 'said lter output a wave for each component image color having a direct current component of such-v a magnitude relative to the peak-to-peak amplitude that the wave has substantially zero values at 120 and 240 degree intervals after each maximum value.

6. In a color television system, apparatus for developing a composite time division multiplex signal wave representative of the color components of successive elemental areas of an image, comprising means for generating concurrently individual Video signals representative respectively of the component image colors, a normally inoperative sampling device for each of said video signals couj peak amplitude that the Wave has substantially zero values' at 120 and 240 degree intervals after eachvmaximum value.

representative of three color components of successive elemental areas of an image, comprising means including a television camera tube for each component image color for generating concurrently individual video signals representative respectively of the component image colors, a normally inoperative gating device coupled to each of said camera tubes, a source of control pulses having a predetermined video signal sampling frequency, means coupling said pulse source to said gating devices to render them momentarily operative successively at 120 degree intervals at said sampling frequency, a video signal adder coupled to the output circuits of all of said gating devices, a low pass lter coupled to said adder and having a cutoff frequency only slightly higher than said sampling frequency, and variable biasing means for each of said gating devices to control the length of the operative periods of said gating devices suitably to produce at said filter output a substantially sinusoidal wave for each compo'- nent image color having a direct current component of such a magnitude relative to the peak-to-peak amplitude that the wave has substantially zero values at 120 and 240 degree intervals after each maximum value.

8. In a three-color television system, apparatus for developing a composite time division multiplex signal wave representative of three primary color components of successive elemental areas of an image, comprising means including a television camera tube for each component image color for generating concurrently individual video signals representative respectively of the component image colors, a normally inoperative gate amplitier coupled to each of said camera tubes, a source of control pulses having a predetermined video signal sampling frequency, means including phase shifting apparatus coupling said pulse source to said gate ampliiiers to render them momentarily operative successively at 120 degree intervals at said sampling frequency, a video signal adder coupled to the output circuits of all of said gate amplifiers, a low pass lilter coupled to said adder and having a cutoff frequency only slightly higher than said sampling frequency, and a variable biasing circuit for each of said gate amplitiers to control the length of the operative periods of said gate amplifiers suitably to produce at said filter output a substantially sinusoidal wave for each component image color havinga direct current component of such a magnitude relative t the peak-to-peak amplitude that the wave 7. In a three-color television system, apparatus for developing a composite time division multiplex signal wave has substantially zero values at 120 and 240 degree intervals after each maximum value.

v9. A color television reproducing system comprising,

, a plurality of image-reproducing elements capable respectively of reproducing the different component colors s or' an image in response to electronic excitation, electron beam-developing means energizable to excite said imagereproducing elements, means continuously impressing upon said beam-developing means a video signal wave having different instantaneous amplitudes representative respectively of the color components of successive elemental areas of an image, means normally impressing a biasing voltage on said beam-developing means to render `it inoperative, and means including an electron tube having its anode circuit coupled to said biasing means and to said beam-developing means and operative concurrently with the reception-ot' said different instantaneous video signal amplitudes to overcome momentarily said biasing means, whereby to render said electron beam operative to excite rsaid image-reproducing elements in a predetermined order.

l0. A ,color television reproducing system comprising,

a plurality of image-reproducing kinescopes capable re,

spectively of Yreproducingthe different component colors of an image in responseto selective electronic excitation, electron beam-developing means for each of said kinescopes including a cathode and a beam intensity control grid energizable to excite said image-reproducing ele" ments, means continuously impressing upon said control grids a video signal wave having diiferent instantaneous amplitudes representative respectively of the color components of successive elemental areas of an image, means` normally impressing individual biasing voltages on said cathodes to render said beam-developing means inoperative, an electron keyer tube for each color having its anode circuit coupled to one of said biasing means and to one of said cathodes and operative momentarily to overcome said biasing means, whereby to render said associated electron beam operative, and means including an electron driver tube for all of said colorkeyer tubes to render said-keyer tubes operative in a predetermined orden.,

l1. A color television reproducing system comprising, t a plurality of different color kinescopes, an electron gun for each of said kinescopes including a cathode and a beam intensity control grid, means continuously impressing upon said control grids a video signal wave having diiferent instantaneous amplitudes representative respec- '.,tively of the color components of successive elemental areas of an image, means including a voltage source normally impressing individual biasing voltages on said cathodes to render said electron guns inoperative, an electron keyer tube for each color having its anode circuit coupled to said voltage source and operative momentarily to overcome said biasing means, whereby to render said associated electron beam operative, means including an electron driver tube operative to produce a series of pulses at a frequency equal to the reproduction rate of elemental image areas, and means including a delay network for impressing said impulses upon said color keyer tubes in a predetermined phase relationship to render said keyerv tubes operative successively.

l2. A color television` system comprising, a source of.

colors, means including a video signal amplier `coupled to said signal source for continuously impressing said three-color video signal wave upon s aid electron gun apparatus, a powersupply, means coupled to said power supply for biasing said electron xgun apparatus normally to an inoperative state, an electron color keyer tube for each of said component image colors coupled to Vsaid v power supply and operative momentarily to reduce the biasing of said electron gun apparatus to render it operative to develop electron beam energy Vof an intensity vdetermined by the instantaneous amplitude of the video signal wave, and means operative concurrently with vthe occurrence of maximum amplitudes .of said individual sine waves to operate said Vcolor keyer tubes in a predetermined order.

13. A color television system comprising, a Source of a three-,color video signal Wave consisting .o f three individual v1,20 degree phase displaced sine Waves of a predetermined color repetition frequency having respective amplitudes ,Varying in accordance with the ,different ,component image colors Aand respective direct current components of such magnitudes that the amplitudes of any two of said individual sine waves is substantially zero when that of the ,other Wave is maximum, `a kinescope for each of the component image colors, an electron gun for each Akinescope including an intensity `control grid, means including a vsingle video signal amplier coupled to' said signal source for continuously impressing said three-color video signal wave upon the grids ,Qf all of said kinescopes, a source of positive voltage, means coupled to said voltage source for biasing said electron guns normally to inoperative states, an electron color keyer tube for each of said 'kinescopes coupled to said voltage source and operative momentarily to reduce the biasing of said electron guns to render the respective guns operative to develop electron beams of intensities determined by the amplitude of the video signal wave impressed upon said control grids, and Ameans operative concurrently with the occurrence of maximum amplitudes of said individual sine waves to operate s aid color keyer tubes in a predetermined order.

14. A color television system comprising, a source of a three-color video signal wave consisting of three individual 120 degree phase ,displaced sine Waves of a predetermined color repetition frequency having respective amplitudes varying in accordance with the different component image colors and respective direct current components of such magnitudes that the amplitudes of any two of said individual sine waves is substantially zero when that of the other Wave is maximum, a kinescope for each of the component image colors, an electron `gun for each v'kinescope 'including a cathode and an 'intensity 2i) control grid, means including a single video signal ampl-iiier coupled to said signal source for continuously im- Pressing said three-color video signal wave upon the grids of all ofvsaid kinescopes, a source of positive voltage,

means including a potentiometer coupled .to said voltage source and to said cathodes for biasing said electron guns normally ,to inoperative states, an electron color keyer tube for each 4ofsaid kinescopes, each of said `keyer tubes h alug an output 4c ircuit .coupled yto said voltage source and ,being operative momentarily to reduce the biasing of said electron guns to render the respective guns operative to develop .electron vbeams .of intensities determined by the amplitude of the video signal wave impressed upon said ,control grids, .and means operative concurrently with the occurrence of maximum amplitudes of said individual sine waves to ,operate said colorkeyer tubes one at a time in a predetermined order.

1 5. A color television receiver including, a plural beam image-reproducing means having a plurality of electron beam-,developing means, means lcontinuously impressing a video signal wave upon said beam-developing means, said video signal wave having different instantaneous `amplitudes at ltimes representative respectively of the light `'and shade values of a black and white image and at other times representative respectively of the color components of successive elemental areas of a color image, means normally impressing biasing voltages on said beam-developing means .to render them inoperative, keyer means operative periodically in response to keying pulses and having output circuits coupled to said biasing means in a manner to overcome said biasing voltages momentarily, said keyer means also having input circuits responsive to vs aid keying pulses in a manner to maintain said keyer means inoperative between keying pulses, and means coupling the Output circuits of said keyer means to sa'id biasing Ameans in a manner to overcome said biasing voltages continuously in response to a sustained interruption of said keying pulses.

References Cited in the fle of this patent UNITED ,STATES PATENTS Fredendall et al Apr. 28, 1953 

